Science Earths magnetic field inversions

[Grover]

its proven by plate tectonics that the magnetic field of the earth somehow rotates 180* periodically (every few thousand years or so), and it is also fact, that following that theory, we are due another flip in recent future (within the next 100+ years).
to this, i ask two questions:

==>do we know how the poles reverse? the field is kinda string, so it should take some serious work to change them

==>what happens when they do flip? aside from compass needles pointing the wrong way, what effect will it have on technology? do aircraft use MAG north, or use GPS to locate 'north'

it made interesting discussion in geography and physics in college, i seem to have brought the idea home with me

 

[Wishbone]

The effect on technology will be pretty much nil, apart from the necessity to update the maps which is done regularly. GPS, INS, astronavigation show you the "true North" (the pole wobbles, gyroscopes drift away, GPS suffers from propagation and clock uncertainties).

 

[Urwumpe]

We are not due for anything... the pattern of reversals is mathematically speaking, completely random.

 

[Hielor]

==>what happens when they do flip? aside from compass needles pointing the wrong way, what effect will it have on technology? do aircraft use MAG north, or use GPS to locate 'north'

I can answer this one...

In the US, the majority of directions are given using magnetic north rather than true north, at least when you're in the cockpit (preflight planning sometimes uses true north before converting). All VORs, for example, are set to point toward magnetic north (and updated every so often as the pole moves).

If the poles were to suddenly switch today, the aviation sector would need to take one of two actions:
- Have all aircraft get new magnetic compasses, and start referring to the new magnetic south pole as magnetic north. GPS devices would probably need a software update. If it was a direct switch (ie, there was no additional polar drift on top of the flip), ground installations wouldn't need to change.
- Update all ground installations to point toward the new magnetic north. GPS devices would still need a software update to keep in sync with everything being updated all at once. Airplanes without GPS wouldn't actually need anything done to them.

I suspect that the first one would be the chosen course of action, since the second one introduces a whole slew of problems, such as the deviation between true north and magnetic north being close to 180 degrees.

I don't think the answer will change much even into the future--I doubt GPS-derived "true north" numbers will ever replace magnetic north, since if you lose power you don't have any way within the cockpit of determining true north, while you do have an easy way of determining magnetic north.

 

[Grover]

although, there is some consistency in the time between swaps, as observed around the mid-atlantic ridge, and according to the more recent observations, by the super-depth submersibles, its been quite a long time since the poles swapped.

@wishbone, you mean that most systems dont use magnetic north? oh good, we done have to worry about planes falling from the sky

 

[Hielor]

@wishbone, you mean that most systems dont use magnetic north? oh good, we done have to worry about planes falling from the sky

Read my post. Planes primarily use magnetic north for navigation, but their ability to fly doesn't depend on the earth's magnetic field, so they're certainly not going to be failing out of the sky if things flip...

 

[Grover]

sorry, you posted yours as i was typing mine

ninja'd

 

[Urwumpe]

although, there is some consistency in the time between swaps, as observed around the mid-atlantic ridge, and according to the more recent observations, by the super-depth submersibles, its been quite a long time since the poles swapped.

Only 750,000 years, which is pretty much nothing since the swaps happen every 1.25 million years on the average.

https://secure.wikimedia.org/wikipedia/en/wiki/Geomagnetic_reversal

Also, I find it pretty funny to use super-depth submersibles for that, in reality the samples are gathered by ships and simple hollow steel rods that are drilled into the sediments by their gravity.

 

[Warped]

Only 750,000 years, which is pretty much nothing since the swaps happen every 1.25 million years on the average.

https://secure.wikimedia.org/wikipedia/en/wiki/Geomagnetic_reversal

Also, I find it pretty funny to use super-depth submersibles for that, in reality the samples are gathered by ships and simple hollow steel rods that are drilled into the sediments by their gravity.

Yeah, but we're majorly over-due for a switch today.

 

[Quick_Nick]

I'm quite sure it wouldn't happen in a day and wouldn't happen without warning.

 

[T.Neo]

Indeed, I would be worried more about the weakening of the magnetic field that would be associated; not only for increased exposure on the surface to radiation, but exposure of astronauts and satellites in Earth orbit... it might be quite problematic.

There won't be a pole shift along with the magnetic reversal... this is not a Roland Emmerich film.

True polar wander does occur, but over a scale of millions of years. If Earth were somehow to do an instant polar shift, a 'la Graham Hancock's "crustal displacement", it would displace, not north to south, but everywhere at the same time. :facepalm:

 

[Hielor]

There won't be a pole shift along with the magnetic reversal... this is not a Roland Emmerich film.

True polar wander does occur, but over a scale of millions of years. If Earth were somehow to do an instant polar shift, a 'la Graham Hancock's "crustal displacement", it would displace, not north to south, but everywhere at the same time. :facepalm:

I was referring to magnetic poles when I talked about shifting

 

[walsjona]

As I understand it it dosn't simply switch (well maybe if you looked at it on a geological time scale), it dies down over time before stopping almost alltogether and then starts up again, much like a freight train changing direction.

Scinetists recon we may already be seeing some of the early effects of a magnetic reversal. The South Atlantic Anomaly is an area where the geomagnetic field has weekened so much that the van allen belt is much closer to the earth in that region.

If the wiki page is anything to go by then it appears this causing problems for spacecraft orbiting over that region

[ame="http://en.wikipedia.org/wiki/South_Atlantic_Anomaly"]South Atlantic Anomaly - Wikipedia, the free encyclopedia[/ame]

 

[Urwumpe]

As I understand it it dosn't simply switch (well maybe if you looked at it on a geological time scale), it dies down over time before stopping almost alltogether and then starts up again, much like a freight train changing direction.

Wrong. It has reduced strength, but doesn't completely stop, because Earth is no simple dipole magnet. It is a complex magnet with many small magnetic poles. Currently, more magnetic north poles are in the northern hemisphere (slowly changing), during the time of reversal, the poles will be wildly mixed.

Scinetists recon we may already be seeing some of the early effects of a magnetic reversal. The South Atlantic Anomaly is an area where the geomagnetic field has weekened so much that the van allen belt is much closer to the earth in that region.

If the wiki page is anything to go by then it appears this causing problems for spacecraft orbiting over that region

Yes, but your reasoning is wrong - the SAA is a normal feature of Earths magnetosphere not related to the geomagnetic reversal. In reality, the slow changes in the magnetic map of Earth is what makes scientists believe that we are already in a reversal process...which could still take a few thousand years.

If my understanding of magnetic fields isn't completely wrong, the SAA would actually move away from the south pole and become a wider spread region if a reversal takes place. Slowly.

 

[walsjona]

Wrong. It has reduced strength, but doesn't completely stop, because Earth is no simple dipole magnet. It is a complex magnet with many small magnetic poles. Currently, more magnetic north poles are in the northern hemisphere (slowly changing), during the time of reversal, the poles will be wildly mixed.

Yes, but your reasoning is wrong - the SAA is a normal feature of Earths magnetosphere not related to the geomagnetic reversal. In reality, the slow changes in the magnetic map of Earth is what makes scientists believe that we are already in a reversal process...which could still take a few thousand years.

If my understanding of magnetic fields isn't completely wrong, the SAA would actually move away from the south pole and become a wider spread region if a reversal takes place. Slowly.

Fair enough. I didn't say I was right :facepalm:.
As it happens I never said it was dipolar I only said that it effectivly stops which to all intense and purposes it does, since although there is still a field present it is very little use to us as humans or for other creatures. Particulary not in a Solar Storm! On the up side we would probably see the spectacular Auroras closer to the equator:thumbup:.

 

[jedidia]

during the time of reversal, the poles will be wildly mixed.

somehow, a century without a clearly defined north pole sounds somewhat worse than it changing direction from one day to the other... :blink:

 

[Urwumpe]

somehow, a century without a clearly defined north pole sounds somewhat worse than it changing direction from one day to the other... :blink:

Much worse - imagine you have a compass that points exactly to north at your home, and in just 500 km distance, you need to correct it by about 180°...

 

[statickid]

MANY consumer grade GPS units only have a magnetic sensor as a higher priced feature. Usually a GPS displays what direction North is based on your movement and has absolutely NOTHING to do with sensing the Earth's magnetic field. In other words it is mathematically inferred by your changing latitude and longitude. You can choose to go by magnetic or true north and when selecting between these options it has to do with pointing to the location. This does not turn on a magnetic compass sensor in these devices, it merely calibrates the map to display correctly depending on any physical map or bearings you are using for a reference.

I have no idea about the high end aviation/shipping instruments. Although if I had to guess they probably use BOTH types of systems for an easy safety redundancy (magnetic and inferred)

 

[Urwumpe]

I have no idea about the high end aviation/shipping instruments. Although if I had to guess they probably use BOTH types of systems for an easy safety redundancy (magnetic and inferred)

Only velocity vector. Attitude is done by other sensors.

For satellites, you need multiple antennas and special receivers for getting coarse attitude information from GPS.

 

[T.Neo]

Maybe a very strong radio transmitter at the geographic north pole, or something like that?

Also, as for geomagnetic reversal being "completely random", see here. Seems that back during the Cretaceous, around 115-85 million years ago, the poles were arranged pretty similar to how they are now (a period of around 30 million years). In more recent times, however, pole shifts have been far more frequent.

It's interesting; during the Cretaceous and Jurassic, we appear get large stable periods, as well as periods of rapid change, in the upper Jurassic and lower Cretaceous (similar to the recent reversals), whereas the Cenozoic is dominated by rapid changes, becoming more and more rapid passing on from the Paleogene and into the current era.